The Seasonality of Consumer Prices

In this paper, we reevaluate the evidence of seasonality in prices which we find to be substantially greater than previous research has indicated. That is, seasonal price movements have become more prominent in the relatively stable inflation environment that has prevailed since 1982. One main conclusion is drawn from this analysis: The amount of seasonality in prices differs greatly by item, making it difficult to generalize about seasonal price movements. A casual reading fails to reveal an easily identifiable origin of the seasonal variation of prices. That is, seasonality in consumer prices is predominantly idiosyncratic in nature, a result that contrasts with studies demonstrating a common seasonal cycle in real economic variables. This finding has an important practical implication: Given the selective, disaggregated approach taken by the Bureau of Labor Statistics to adjust data seasonally, the existence of idiosyncratic seasonality increases the likelihood of allowing noise in the aggregate CPI at a seasonal frequency. This argues in favor of seasonally adjusting the index after aggregation.